New Insights into Structure and Luminescence of Eu^III and Sm^III Complexes of the 3,4,3-LI(1,2-HOPO) Ligand

We report the preparation and new insight into photophysical properties of luminescent hydroxypyridonate complexes [M^III<b>L</b>]⁻ (M = Eu or Sm) of the versatile 3,4,3-LI­(1,2-HOPO) ligand (<b>L</b>). We report the crystal structure of this ligand with Eu^III as well as insights into the coordination behavior and geometry in solution by using magnetic circular dichroism. In addition TD-DFT calculations were used to examine the excited states of the two different chromophores present in the 3,4,3-LI­(1,2-HOPO) ligand. We find that the Eu^III and Sm^III complexes of this ligand undergo a transformation after in situ preparation to yield complexes with higher quantum yield (QY) over time. It is proposed that the lower QY in the in situ complexes is not only due to water quenching but could also be due to a lower degree of f-orbital overlap (in a kinetic isomer) as indicated by magnetic circular dichroism measurements

Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1‑Hydroxypyridin-2-one Complexes in Aqueous Solution

A series of 10 tetradentate 1-hydroxy-pyridin-2-one (1,2-HOPO) ligands and corresponding eight-coordinated photoluminescent Eu­(III) and Sm­(III) complexes were prepared. Generally, the ligands differ by the linear (nLI) aliphatic linker length, from 2 to 8 methylene units between the bidentate 1,2-HOPO chelator units. The photoluminescent quantum yields (Φ_tot) were found to vary with the linker length, and the same trend was observed for the Eu­(III) and Sm­(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φ_totxε). The change in ligand wrapping pattern between 2LI and 5LI complexes observed by X-ray diffraction (XRD) is further supported by density functional theory (DFT) calculations. The bimodal Φ_tot trends of the Eu­(III) and Sm­(III) complexes are rationalized by the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length

Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1‑Hydroxypyridin-2-one Complexes in Aqueous Solution

A series of 10 tetradentate 1-hydroxy-pyridin-2-one (1,2-HOPO) ligands and corresponding eight-coordinated photoluminescent Eu­(III) and Sm­(III) complexes were prepared. Generally, the ligands differ by the linear (nLI) aliphatic linker length, from 2 to 8 methylene units between the bidentate 1,2-HOPO chelator units. The photoluminescent quantum yields (Φ_tot) were found to vary with the linker length, and the same trend was observed for the Eu­(III) and Sm­(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φ_totxε). The change in ligand wrapping pattern between 2LI and 5LI complexes observed by X-ray diffraction (XRD) is further supported by density functional theory (DFT) calculations. The bimodal Φ_tot trends of the Eu­(III) and Sm­(III) complexes are rationalized by the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length